“It’s 4 a.m. in Iowa so I’m running,” Grassley said in a predawn tweet that included an image of him jogging. “I do that 6 days a week. Before I start the day I want you to know what Barbara and I have decided. I’m running for re-election — a lot more to do, for Iowa. We ask and will work for your support. Will you join us?”

The decision by Grassley, who has served in the U.S. Congress since Jimmy Carter’s presidency, boosts Republican prospects for holding the seat next year, when control of the chamber will be at stake. Recent polling has shown Grassley with a sizable lead over Democratic challenger Abby Finkenauer.

Perhaps Grassley’s most consequential impact on the country has been his recent tenure as chairman of the Senate Judiciary Committee, a position that gave him significant influence in pushing through the nominations of dozens of judges during the Trump presidency as well as three Supreme Court justices, including the divisive nomination of Brett M. Kavanaugh.